STOCKHOLM, July 20 (Reuters) - Drugmaker Swedish Orphan Biovitrum (Sobi) said on Friday it had reached an exclusive licensing deal with Swiss firm Novimmune SA for the perpetual global rights to emapalumab, a late-stage orphan drug candidate for the treatment of primary Haemophagocytic lymphohistiocytosis.

Sobi said emapalumab provided an attractive near-term commercial opportunity for the company with sales potential from 2019 onwards, and with an estimated annual 2.5 billion-3.0 billion Swedish crowns ($282 million - $338 million) peak sales potential.

Haemophagocytic lymphohistiocytosis is a rare and life-threatening syndrome of extreme immune activation, and the primary form of the disease mainly occurs in infants and young children.

Sobi said it would make an upfront cash payment of 50 million Swiss francs ($50 million), with a total of 400 million francs in additional payments over an eight-year period.

It said additional payments might be accelerated by either party at any time after July 1, 2019.

"We believe this transaction is an excellent fit for Sobi and consistent with our strategy of expanding our commercial Specialty Care portfolio," Sobi CEO Guido Oelkers said in a statement.

The Swedish firm also said it had signed a non-binding letter of intent for a possible subsequent acquisition of all emapalumab assets, including the transfer of relevant employees. ($1 = 0.9989 Swiss francs) ($1 = 8.8702 Swedish crowns) (Reporting by Johannes Hellstrom Editing by Edmund Blair)